The invention relates to a compressed-air-driven double diaphragm pump consisting of a pump housing having two housing chambers disposed side-by-side in a spaced-apart relationship, having each a diaphragm assembly and being divided by the latter into a pumping chamber and an air chamber, the air chambers of the two housing chambers being aligned with one another and having between them a compressed air control means which feeds compressed air to the two air chambers and alternatively vents the air chambers, the pump chambers being communicated by valve means with a suction connection and a discharge connection through which the material to be pumped is aspirated into the pump chamber on the basis of the diaphragm movement produced by the compressed air or is forced out of the pump chamber, the compressed air control means having a main valve control piston for the reversal of the air chamber connection paths.
Such compressed-air-driven double diaphragm pumps are already known in a variety of forms.
For example, the applicant's Letter of Information LP 004 shows a diaphragm pump of the kind represented in FIG. 1. Such compressed air diaphragm pumps are especially suitable for severe pumping duty, such as for example the pumping of sludges, pulps, dusts and the like. The advantage of such diaphragm pumps lies in the fact that they require no rotating parts and no shaft seals, and they can be run dry without damage. Diaphragm pumps of this kind are non-priming and can be used for either surface or underwater operation. In particular, however, they can also be operated against closed discharge lines without an additional overflow valve.
On account of the compressed-air drive, separate driving means with their required base plates and couplings are unnecessary. Diaphragm pumps of the kind described above are especially compact and easy to transport, and can be used independently of other power sources, such as especially electrical power.
Since no sliding or rotating parts operating in close tolerances are necessary and the velocities of movement are low, abrasive, viscous and shear-sensitive media can be pumped without difficulty.
By changing the rate of delivery of the compressed air the pump also can be regulated very simply, without the need for expensive and complex regulating means.
However, the compressed air control means, which is represented in FIG. 2, has still been offering problems. The control valve piston used in the known apparatus as shown in the drawing operates as a two-position valve, which alternately communicates the air chamber represented on the left in FIG. 1 through the outlet with the free atmosphere, and, when reversed, it vents the right air chamber.
The always abrupt venting results in loud air noises and therefore in very noisy operation of the pump. Another environmentally undesirable circumstance is the fact that the oil mist drawn into the drive air from the oil tank to lubricate the piston is undesirably mixed with the exhaust air and can contaminate the surroundings of the diaphragm pump adjacent the exhaust, unless expensive traps and filters are provided. Lastly, at certain positions of the control valve piston a direct path is created between air in areas under the operating pressure and those areas of the pressure control system that are under atmospheric pressure, so that in these valve positions an undesirable loss of compressed air takes place.
Compressed air losses furthermore occur due to the clearances between piston and casing, which cannot be greatly reduced, and which despite the oil lubrication cannot entirely prevent the passage of compressed air.
To sum up, it can be said that the known compressed-air driven double diaphragm pump represented in FIGS. 1 and 2 is of extraordinary simple construction and very rugged, but it does have a very low efficiency and has an adverse effect on the environment due to noise and oil mist.